Facing Spring Frost Damage in Grapevine: Recent Developments and the Role of Delayed Winter Pruning – A Review.

Abstract

In this review, we briefly discuss factors conducive to an increased spring frost risk in viticulture and provide updates on vine susceptibility to frost events and damage assessment. The core of the review, though, deals with a physiological oriented tool of prevention of the frost damage consisting in a delayed winter pruning (i.e. executed at or beyond the “wool” bud stage) aimed at postponing bud burst. The exploited principle is related to the inherent acrotony of the grapevine which would “sacrifice” the already developing apical shoots to an incurring frost, while basal nodes will be preserved as being still dormant. A survey conducted on 21 published papers confirms tha, final pruning performed not later than 2-3 unfolded leaves borne on apical shoots would achieve a bud burst delay of about 15-20 days, while yield is mildly affected. At times, such a delay can carry on until harvest, thus postponing fruit maturity into a cooler period of the year. Most recommended late winter pruning protocols envisage a two-step intervention. In spurred cordons, a mechanical pre-cut aimed at shortening canes at 7-8 nodes while also performing wood shredding, can be made anytime during the dormant season. Thereafter a final hand spur shortening is made at the suitable developing stage of the apical shoots. In a cane-pruned vine, previous year fruiting cane(s) can be removed any time in winter while selecting at least two canes that must be kept vertical and longer that the required spacing-dictated length. Shortening of the two canes along with horizontal positioning should take place no later than the 2-3 unfolded leaves borne on the apical end of last seasons shoots.